Rebels, government forces say at least four people have been killed in recent shelling

MOSCOW—The Russian and Ukrainian governments traded allegations Monday over an uptick in violence in eastern Ukraine, as Russian President Vladimir Putin paid a visit to the Black Sea peninsula that Moscow annexed from its neighbor last year.

Russian-backed rebels and Ukrainian forces in recent days escalated shellfire despite a cease-fire agreement reached in February. Russian Foreign Minister Sergei Lavrov blamed the Ukrainian government for the intensified fighting, saying Kiev’s forces were apparently preparing for a fresh...